RDMA/rtrs: Cleanup unused 's' variable in __alloc_sess

Link: https://lore.kernel.org/r/20210325153308.1214057-18-gi-oh.kim@ionos.com


Signed-off-by: Jack Wang <jinpu.wang@ionos.com>
Signed-off-by: Gioh Kim <gi-oh.kim@ionos.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>